The invention relates to a method of and a system for determining the speed, distance traversed, elapsed time, average speed, calories expended by a person or animal while running or walking. The invention further relates to an athletic or hiking shoe for use in the system or method.
In the past years it has been clearly shown that regular exercise is an important factor against cardiovascular illnesses. Further it has been shown that regular exercise has a positive effect on the mental condition of a person. Many individuals therefore turned to their own fitness program of regular jogging, running or walking. Running has been recognized for its therapeutic effects on the body. It increases cardiopulmonary fitness, helps lower the blood pressure, decreases cholesterol associated with heart disease and reduces weight. Because of the growing popularity of walking, jogging and running, the number of devices aiding those people who walk, jog or run, is growing as well. Devices already common to the market place are those which are generally called step counters or pedometers. If the stride length of a runner or walker is constant, the step counter gives a measure of the speed of the runner or walker and the distance traversed. However, the stride length is in general not constant and certainly not for various speeds, and thus, these devices are not very accurate.
There are devices known in the prior art which measure the speed of the runner without input of the stride length. One of these methods is described in U.S. Pat. No. 4,578,769, which calculates the running or walking speed by measuring the contact time between the shoe and the ground. However, the relationship between contact time and speed is only linear for running speeds above 8 km/h. An accurate determination of the walking speed and the distance traversed while walking is not possible with this device. Moreover said relationship and said determination is dependent on the person.
A more accurate device is known from International Application No. WO 97/21983. In this known device accelerometers and rotational sensors and an electronic circuit that performs mathematical calculations to determine the distance and height of each step are placed in the sole of one shoe of the runner. This known device employs three acceleration and three rotational sensors for measuring the displacement of the runner""s foot. it will be appreciated that this known device is complicated and relatively expensive.
It is an object of the invention to provide a new and improved measuring method and system for a running aid which overcomes disadvantages of the prior art devices and which is relatively inexpensive and simple and convenient to use.
A further object of the invention is to provide a running aid with which the speed of the runner can be easily and accurately determined.
A still further object of the invention is to provide a running aid with which the distance traversed by the runner can be easily and accurately determined.
Another object of the invention is to provide a running aid with which the average and maximum speed, total distance traversed by the runner, stride length of the runner, elapsed time, number of calories expended by the runner can be easily and accurately determined.
To obtain the above and other objects, according to the present invention, there is provided a system for measuring performance during an exercise activity comprising: an acceleration sensor for measuring acceleration in a moving direction of a foot of an exerciser and for providing an acceleration signal in response to said acceleration; signal processing means comprising: means for analyzing a waveform of the acceleration signal and for determining from the analyzing a beginning and an end of movement of the foot during a stride made by the foot of the exerciser; means for single integrating and for double integrating the acceleration signal between said beginning and said end of movement in order to compute the speed of the foot as a function of time during the stride and the distance traversed by the foot as a function of time during the stride, respectively; means for computing an acceleration error by equalizing the acceleration error with the speed at the end of the movement of the foot divided by the time lapsed between the end and the beginning of the stride; means for computing a distance error by double integrating the acceleration error over said time lapsed between the end and the beginning of the movement of the foot; means for computing a corrected distance by subtracting the distance error from the distance traversed during the stride.
The method used in the invention to determine the speed and the distance traversed while running or walking is based on a constant monitoring of the acceleration of a foot of the runner or walker. This is done by minimally one accelerometer attached to the foot or shoe or mounted in a shoe of the runner which measures the acceleration in the forward direction, parallel to the line between the toes and heel of the foot or between the nose and the heel of the shoe if the forward speed and stride length of the runner is to be monitored; or in a direction perpendicular to that direction if the vertical speed and jump height of the runner is to be measured; or in any direction in which one is interested to measure the performance during an exercise. The signal generated by the accelerometer is processed and analyzed.
The algorithm used to interpret the acceleration signal consists basically of three main functions, i.e. the determination of the beginning and end of a stride, the double integration of the acceleration signal, and the correction of the double integrated signal. The determination of the beginning and end of the stride is done by analyzing the waveform of the acceleration signal. Single integration of the acceleration signal between the beginning and end results in the speed of the foot as a function of time, while the double integration of the acceleration signal gives the distance of the foot as a function of time.
However, the acceleration sensed by the acceleration sensor is not the same as the true acceleration of the foot or shoe in the walking or running direction. Because of the constantly changing angle between the foot or shoe and the ground, there is a complicated relationship between the acceleration in the walking or running direction and the acceleration sensed by he acceleration sensor. Further, because of this changing angle, also the gravitational acceleration results in an extra complicating signal. However, the inventors have realized that one does not need to know the angle as a function of time when a further condition is used.
At the end of the stride the velocity of the foot or shoe is zero, because it has landed on the ground. The result of the single integration of the acceleration signal from the beginning of a stride to the end of a stride, i.e. the velocity of the foot or shoe at the end of the stride, however, is not equal to zero due to the extra component in the acceleration signal. This extra component is calculated from the speed at the end of the stride and used to compute a corrected distance traversed during the stride. The speed of the runner is calculated by dividing the corrected distance by the time lapsed between successive strides. In this way the distance traversed and the speed of the runner can be measured accurately without making use of a plurality of acceleration and rotational sensors.
By inputting personal data, such as the mass of the exerciser, it is possible to compute the number of calories expended by the exerciser. By adding a heart rate monitor and combining heart rate data and the calories expended by the exerciser per unit of time a number can be generated which is representative of the fitness or condition of the exerciser. The running aid system may further comprise a display unit worn around the wrist or somewhere else which displays data such as current speed, stride length, elapsed time, average speed, maximum speed, total distance traversed, calories expended and fitness indication. The communication between the unit comprising the acceleration sensor and the signal processing means and the display unit is preferable done by means of a wireless transmitter in the sensor unit and a receiver in the display unit.
The acceleration sensor may be incorporated in a unit to be attached to the foot of the exerciser. This unit can also be incorporated in the sole of an athletic shoe. This unit may further comprise the signal processing means and the transmitter.